The invention relates to turbine rings for gas turbines, whether industrial gas turbines or gas turbines forming aeroengines.
In a gas turbine, a turbine ring defines a flow section at a rotary wheel of the turbine for a stream of hot gas passing therethrough. In order to ensure the best possible efficiency, it is important to avoid gas passing directly between the tips of the blades of the turbine wheel and the inside surface of the ring. Thus, in the usual way, a turbine ring is provided on its inside face with a layer of abradable material with which the turbine tips can come into contact without significant damage under the effect of dimensional variations of thermal origin or as the result of the centrifugal force that is applied to the blades.
Turbine rings are usually made as a plurality of adjacent sectors of metal material.
For example, document U.S. Pat. No. 6,758,653 proposes replacing the metal material of the turbine ring sectors by a thermostructural composite material, and more particularly by a ceramic matrix composite (CMC) material. Such a material presents mechanical properties that make it suitable for constituting structural elements and also has the ability to conserve these properties at high temperature, while presenting density that is much lower than that of the metal materials commonly used in such an application.
It is therefore attractive to replace the metal material of the turbine ring sectors with a CMC material. Nevertheless, it is necessary to design an assembly for the ring sectors that is rather complex in order to accommodate the difference between the coefficients of expansion of a CMC material and of the material of a metal casing in which the ring sectors are assembled, and while minimizing leaks against adjacent sectors. Such an assembly of CMC ring sectors in a metal ring is described in document EP 1 350 927.
Document GB 2 343 224 shows a CMC ring of C-shaped section with curved ends that press against outwardly-directed radial surfaces of a metal annular block, which ends are kept pressed against these surfaces by resilient elements. It is therefore necessary to make the CMC ring in a shape that is relatively complex and to use a metal support block that is segmented.
Document US 2005/158168 discloses a CMC ring of U-shaped section with ends that are connected to lateral faces of an annular metal block by means of connection parts of a special design that accommodates relative movement. In order to enable the CMC ring to be assembled, either the ring or the annular metal support block must be made as a plurality of annular segments.